Tunnel’s two nerve centers taking shape

State-of-the-art systems will be the key to maximizing safety and efficiency inside the SR 99 tunnel. Lighting and intelligent transportation systems (video cameras, traffic counters, variable message signs, etc.) will help ensure smooth traffic flow, while the ventilation, drainage and fire-suppression systems will help the tunnel meet the highest safety standards. To manage these systems, we’ll need nerve centers at each end of the tunnel. While they’re hard to see now, those nerve centers – we call them north and south portal operations buildings – will soon rise from the ground.
The south operations building will sit on the south side of South King Street, just to the north of the tunnel entrance. Visible to northbound drivers, it will house maintenance vehicles, ventilation fans and emergency power. Below is a rendering of the building.
A site visit today wouldn’t show you much because four stories of the building rest underground. Much of the underground structural construction is complete, and crews are beginning to install electrical systems while the building rises above the surface. 
The north operations building will be located at the corner of Harrison Street and Sixth Avenue North, just to the south of the tunnel entrance. This building will house maintenance facilities, repair shops, radio equipment, the operations center, offices and crew rooms. Maintenance crews will primarily report to and work out of this building, which will also have a small parking lot.
Construction is underway on the north portal building, with crews currently building the underground structures for the ventilation and vehicular elevator shafts, and beginning work on the ground-level building that sits atop the cut-and-cover portion of the tunnel. Drivers and transit riders taking Aurora Avenue North can see the construction site running parallel on the west side of the Seattle Pacific Hotel. 

Below is a rendering of the north portal operations building as it will appear to southbound traffic entering the tunnel.

The yellow stacks, each rising 102 feet above street level, are part of the centrifugal ventilation fans that will be prominent features of both buildings. Each operations building will have four fans, and each fan will be capable of moving 160,000 cubic feet of air per minute. To give you a sense of that volume, the eight fans would have been able to recycle all the air inside the old Seattle Kingdome (67 million cubic feet) in a little under an hour. 
The buildings will also provide crews with direct access to the tunnel via freight elevators, and serve as the end points for the tunnel corridors that provide passage for utilities and emergency egress. Interesting fact: Both buildings will be built to specifications that match LEED Silver standards, but the designation won’t be official because there is no applicable category within the LEED certification system for these buildings – turns out they’re two of a kind.